1. Technical Field
The present invention relates to a developing apparatus which is provided with a toner supporting roller that supports electrification toner on the surface thereof, an image forming apparatus, an image forming method which forms an image by using the roller, and toner.
2. Related Art
In the technology of developing an electrostatic latent image by toner, in general, toner is supported on the surface of a toner supporting roller formed into an approximately cylindrical shape. In such a kind of technology, since variation inevitably occurs in the electrification amount of toner, in particular, toner having a low electrification amount, or toner electrically charged so as to have the opposite polarity to the original electrification polarity is adhered to the portion of an image, to which toner should not be essentially adhered, so-called fogging thereby occurring. Therefore, there is a technology which, in order to increase the electrification amount of toner which is supported on the surface of a toner supporting roller, uses toner having conductive property as toner, and also, is configured so as to give electric charges to the toner of the surface of the toner supporting roller by disposing an electric charge injecting member applied with bias voltage having the same polarity as the electrification polarity of toner, so as to face the toner supporting roller (for example, FIG. 1 of JP-A-2005-331780).
However, according to an experiment conducted by the inventors of this application, in the technology described in JP-A-2005-331780, since an electric field due to the bias voltage applied to the electric charge injecting member acts in a direction that pushes previously charged toner to the toner supporting roller side, a toner transportation amount on the toner supporting roller is increased. As a result, the amount of toner, into which electric charges are to be injected, is increased, so that an electrification amount as a whole is increased. However, it cannot be said that the effect of suppressing variation of the electrification amount of individual toner is sufficient.